1. Field of the Invention
The present invention relates to a multi-chamber pacing system of the type having a pulse generator for successively delivering pacing pulses to chambers of a patient's heart, and evoked response detectors having blanking intervals following the delivery of pacing pulses and including sensing elements for sensing IEGM signals from each of the heart chambers and an integrating unit that integrates the IEGM signal within evoked response detection time windows after delivery of pacing pulses for detecting evoked response, the evoked response detection time window for a heart chamber containing at least one blanking interval resulting from delivery of a pacing pulse to another chamber, and each of the sensed IEGM signals having a generally known morphology.
In the following, “chambers of the heart ” denotes right and left atria as well as right and left ventricles of the heart.
2. Description of the Prior Art
U.S. Pat. No. 6,148,234 disclose a dual site pacing system, either bi-ventricular or bi-atrial, wherein signals are sensed during the refractory period following delivery of stimulation pulses. Pacing pulses are delivered substantially concurrently to both the heart chambers, although it is mentioned that for patients with an intra-atrial block, the left atrium may be stimulated up to 90 msec later than the right atrium. If capture is achieved in both chambers no intrinsic depolarization signals can be generated during the following biological refractory period of the cells of he heart. If, however, the threshold of one heart chamber has risen above the level of the delivered pulses, that chamber will not be captured and will not have a biological (heart cell) refractory period following that delivery of the pulses. In this case, for patients having a conduction delay from one chamber to the other, the propagated signal from the other chamber will be sensed in the non-captured chamber during the pacemaker refractory period, that is started by the stimulation pulse delivered to the other chamber. Such sensing during the pacemaker refractory period is interpreted to be the result of loss of capture.
If two heart chambers are stimulated at somewhat different times, one of the chambers will be blanked when the other one is stimulated. Most pacing systems are constructed such that all signal channels are blanked when a stimulation pulse is emitted. Consequently there will be an interruption in sensed IEGM signals and that will influence the evoked response signals obtained by integration of the IEGM signals. This occurs in all dual or multi chamber pacing systems, e.g. at both bi-ventricular and bi-atrial pacing. If sensed signals are integrated in an evoked response detection time interval from e.g. 4 msec to 50 msec after stimulation to determine evoked response, and if a stimulation of the other chamber takes place at 10 msec after the first stimulation, there will be an interruption of the signal in the above mentioned detection time interval.